RT Journal Article
T1 Diagénesis y estratigrafía secuencial de la arenisca «U» de la Fm Napo del Oriente, Ecuador
T1 Diagenesis and sequence stratigraphy of the "U" sandstone from the Napo Formation, Oriente basin, Ecuador
A1 Estupiñán Letamendi, Jenny
A1 Marfil Pérez, Rafaela
A1 Permanyer, Albert
AB The Napo Formation of Cretaceous age in the Oriente basin, Ecuador, is an important sandstone reservoir. The«U» sandstone is one oil interval within the Napo Formation. It is buried at a depth of 1500 m in the easternpart of the basin and down to 3100 m in the western part. This sandstone display higher porosity values (av.20%) than other reservoirs in the region. The sandstone was deposited in fluvial, transitional and marineenvironments, and their correlation with the sequence stratigraphy is related to HST, LST, TS. «U» sandstone isfine to medium grained quartzarenite and subordinate subarkose. The principal cements are carbonates, quartzovergrowth and kaolin, with scarce amounts of pyrite and chlorite. Carbonate cements include: Eogeneticsiderite (S1), mesogenetic and post-compactional calcite, Fe-dolomite, ankerite and siderite (S2). Early sideritehelped to retain porosity by supporting the sandstone framework against compaction. Dissolution of feldsparsand mesogenetic carbonate cements is the main mechanism for secondary porosity development duringmesodiagenesis. The stable isotope composition of the S1 siderite are consistent with precipitation from meteoricwaters. The anomalous low ä18O‰ values of some of these carbonate phases could reflect the replacementand recristalization from S1 to S2 siderite at deep burial and high temperature. However, due to this higher Mgcontent, siderite S2 could have precipitated as a result of the thermal descarboxilation of the Mg rich organicmatter. The last carbonate cements to precipitate were dolomite/ankerite. The negative ä18O‰ in these cementsis related to the continued precipitation at higher temperature and burial depth
YR 2006
FD 2006
LK http://hdl.handle.net/10272/8595
UL http://hdl.handle.net/10272/8595
LA spa
DS Repositorio Institucional de la Universidad de Huelva
RD 30 may 2026